Enhancement of polarization isolation in a dual polarized antenna



QnFzQ um Nov. 17, 1970 z. G. LYON ET AL 3,541,560 ENHANCEMENT OF POLARIZATION. ISOLATION IN A DUAL POLARIZED ANTENNA Filed June 24, 1968 PR 00 0:7 NC

0 R RECE/ w/vq MEANS INVENTORS ZNO LYON JOHN G ANLUND BYROBERT J.- M'RKEL ATTORNEY United States Patent ABSTRACT OF THE DISCLOSURE Means is provided for enhancing polarization isolation wherein at least one conductive probe is mounted in front of the mouth of a waveguide horn. The probes mounting permits selective interception of the orthogonal waves passing through said horn.

BACKGROUND OF THE INVENTION In general this invention relates to means for enhancing isolation between two orthpgonally polarized waves on a line-of-sight path, and more particularly to means for cross coupling power between two channels of a dual polarized feed horn to compensate for the depolarized signal.

Means is required to compensate for depplarization caused by non-ideal transmission media and/or equipment so that the isolation between the two channels of a dual polarized feed is constant. It has been found that the propagation medium is fairly stable so that long-term improvement can be obtained with the means according to the invention Without continual readjustment of the equipment. The significance of this means is its ability to improve the isolation between two independently transmitted waves on the same frequency to a point where two pieces of information can be transmitted on two waves. This will effectively double the bandwidth of the microwave system without incurring a penalty on the spectrum utilization.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide means of enhancing the isolation between two orthogonally polarized waves.

According to the broader aspects of the invention, there is provided a conductive probe mounted in the front of the mouth of a waveguide horn, the probe being positioned so that it can be displaced relative to the mouth of said horn so as to be selectively interposed in the path of the orthognal waves passing through said horn, thereby enhancing the isolation between said two waves.

BRIEF DESCRIPTION OF THE DRAWING The following description will be more easily understood if reference is made to the accompanying drawing in which:

FIG. 1 illustrates an arrangement according to the invention; and

FIG. 2 illustrates a view taken along lines 2-2 of FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is provided a square waveguide horn to which is coupled means 11 for producing or receiving vertically polarized waves 12 and horizontally polarized waves 13. The polarized waves 12, 13 may be produced by said means for transmission, or coupled to said means for reception and processing.

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Opposite the mouth 14 of the waveguide horn 10 is positioned a reflector 15 which may or may not be used in. the arrangement of the invention. To the mouth 14 of the feed horn 10 is positioned a flange 16 on which is mounted an electrically insulative rod 17. The rod 17 mounts an electrically conductive wire probe 18 which is displaceable, in the direction of arrows 19, in a plane parallel to the mouth 14 of the feed horn.

Referring additionally to FIG. 2, typically in the mouth of the feed horn is shown two orthogonal waves 20 comprising a vertically polarized E wave and a horizontally polarized E wave. Around the flange is positioned a movable band 21 and in the band is positioned the rod 17. The band and rod are rotatable about the mouth of the horn as indicated by arrows 22. In addition, the probe is pivotable about point23 of the rod 17 as indicated by arrows 24. The probe may also be inserted across the mouth of the horn or withdrawn from mouth of the horn as indicated by the arrows 25. Means 26 are attached to the band and around the rod so that when the empirically selected position for the desired degree of isolation has been found, the probe is set by the fixing means 26 for long term stability of transmitting or receiving the two polarized waves.

The arrangement shown was utilized on a number of line-of-sight paths and proved that it is possible to obtain long term improvement by cross coupling power between the two channels of the dual polarized feed horn to compensate for (null-out) the depolarized signal. Data were collected at 4.4 gHz. using dual polarized feed horns and parabolic reflectors having 3.5 half-power beam widths. The measurements were made by alternately transmitting the two orthogonally polarized carriers; at the receiving terminal two receivers were used for simultaneous recording of the transmitted wave and its depolarized component.

The collected data was analyzed on the basis of the quarter-hourly median values of the depolarized wave. Both long term and short term variations were noted and these were attributed to temporal variations in the refractive index of the atmosphere. Short term variations were especially apparent during rain showers and during periods of atmospheric turbulence. The direct-to-depolarized signal ratio in each channel approximated a log-normal distribution, especially during stable meteorological conditions.

During the tests it was found that long term improvements in the polarization isolation could be obtained by modification of the equipment to allow adjustment of the polarization isolation in the antenna feed horns. Extrapolation of the data indicates that on paths with good Fresnel Zone clearance up to 30 miles long, each of the orthogonally polarized channels can provide at least 19 db 99.9 percent of the time. On paths with poor clearance, extrapolation of the data indicates a minimum of 13 db 99.9 percent of the time.

The probe was attached at the mouth of the feed horn by a rod which was secured by a movable band to allow the rod to be positioned around the periphery of the flange. The probe was able to pivot about the rod and be inserted across or retracted from the mouth of the feed horn. It should also be evident that the device shown was fabricated in a simple manner to be external to the mouth of the feed horn, but it could also be made as an integral part so that the adjustments are incorporated within the feed horn itself, moreover, it may be desirable to independently adjust each channel by utilizing two probes rather than one as described in the preferred embodiment. Any of these variations on the principle disclosed herein should be more than evident to one skilled in the art.

-We claim:

1. Means for enhancing polarization isolation comprising:

awaveguide'horn'adapted for passing vertically and- I horizontally polarized waves through its mouth;

at least one conductive probe mounted in a displaceable parallel plane to the mouth of said horn; and

mounting means for selectively changing the degree of interception of said waves by said probe in a given plane.

2. Enhancement of isolation between two orthogonally polarized waves comprising:

a square waveguide horn positioned to pass said waves through the mouth thereof; a conductive probe mounted in front of the mouth of said horn; and means for mounting said probe in a displaceable manner relative to the mouth of said horn so as to be selectively interposed in the path of said waves, thereby enhancing the isolation between them. 3. Means for enhancing polarization isolation between vertically and horizontally polarized waves comprising:

a square waveguide horn; mounting means on the mouth of said horn, said means being rotatable about the mouth of said horn; a probe pivotably mounted to said means in a parallel plane to the mouth of said horn; and said probe being displaceable from the mouth of said horn and selectively insertable across the mouth thereof to eifect the desired isolation between said waves. 4. The means of claim 3 including means for producing or receiving vertically and horizontally polarized waves being coupled to said horn.

said probe being displaceable and selectively insertable across the mouth of said horn to eflect the isolation between said waves.

7. The means of claim 6 including means for producing or receiving vertically and horizontally polarized waves being coupled to said horn.

8. The means of claim 7 including reflecting means positioned opposite said probe and horn for directional focusing of said waves.

9. The means of claim 6 wherein said rod is an electrically insulating rod.

10. The means of claim 9 including fixing means for fixing the selected position of said probe across the mouth of said horn.

References Cited UNITED STATES PATENTS ELI LIEBERMAN, Primary Examiner US. Cl. X.R. 34378l, 909 

